In the past, for example, as shown in JP-A-2003-92576 publication, known was such a method that, in a road-vehicle communication system, a roadside apparatus generates an IP address (Internet Protocol Address) including an in-vehicle apparatus identifier which was obtained from an in-vehicle apparatus, and that IP address is notified to the in-vehicle apparatus to thereby assign the IP address to the in-vehicle apparatus, which is then connected to Internet.
According to this method, at the time of DSRC (Dedicated Short Range Communication) initial connection request from the in-vehicle apparatus, the roadside apparatus obtains the in-vehicle apparatus identifier LID (Link Identifier) which is defined in ARIB-STD-T75 (basis standard of DSRC communication technology in Japan. Hereinafter, inscribed as T75), and combines it with network prefix to generate an IP address, and at the time of DSRC initial connection response, overlaps the IP address with transmission data, and then, notifies it to the in-vehicle apparatus.
Therefore, according to this method, new communication sequence is not required for assigning an IP address, and communication by means of communication protocol for specifying an in-vehicle apparatus by use of LID and communication by means of communication protocol for specifying an in-vehicle apparatus by use of an IP address become possible.
However, in a conventional road-vehicle communication system, in case of the assumption that an application which was loaded in a roadside apparatus carries out data communication with an application which was loaded in an in-vehicle apparatus by use of a first communication protocol (e.g., IP series communication protocol for specifying an in-vehicle apparatus by use of an IP address), and a second communication protocol (e.g., non-IP series communication protocol for specifying an in-vehicle apparatus by use of LID), an application of a roadside apparatus does not handle an identifier which specifies an in-vehicle apparatus by the first communication protocol (e.g., IP address) and an identifier which specifies an in-vehicle apparatus by the second communication protocol in combination, and therefore, there was a problem that a roadside apparatus can not specify an arbitrary in-vehicle apparatus by use of both communication protocols.
Therefore, this means that, an application in which a number of 2 or more communication protocols are used in parallel generates a problem that it becomes more difficult to specify an arbitrary in-vehicle apparatus.
Also, on the occasion of assigning Ipv4 (Internet Protocol Version 4) to an in-vehicle apparatus, there is a necessity to carry out assignment of an IP address after data length was shortened to LID by use of a hash function etc. That is, in case of assigning, for example, an IP address with class B, to LID which is represented by 32 bits, 16 bits are of a host address, and therefore, there is a necessity to make LID 16 bits by use of the hash function. On that account, there was a problem that there is a possibility of giving an identical IP address to different vehicles erroneously, respectively.